Showing papers on "Pulse duration published in 1973"

Analysis of multiple pulse NMR in solids. II

Abstract: A systematic method, an extension of the average Hamiltonian formalism, is presented for calculating the effects of pulse errors and imperfections in the multiple pulse nuclear magnetic resonance experiments. Application of this method to account for effects of pulse nonidealities such as phase errors, phase transient effects, pulse size errors, and rf inhomogeneity is found to agree with experimental observation, and the results furnish a basis for understanding the complex couplings between the pulse errors and other interactions such as the dipolar and the chemical shift Hamiltonians.

Effect Of Normal Moveout On A Seismic Pulse

Abstract: Using a synthetic seismogram as input, normal moveout correction stretches a reflection pulse in such a way that the spectrum of the pulse is a linearly compressed version of the uncorrected pulse spectrum. The amount of compression depends on t0, the source‐detector separation, velocity, and the rate at which velocity varies with t0. The amplitude of the spectrum is increased by the same factor that expresses the spectral compression. As a result, the summed pulse from a CDP stack is richer in low frequencies than one might anticipate and has a smaller signal‐to‐noise ratio than the square root of the number of traces in the stack.

Dependence of laser‐induced breakdown field strength on pulse duration

Abstract: Field strengths at which optical damage is initiated in NaCl have been measured with a mode‐locked Nd: YAG laser with pulse durations of 15 and 300 psec. Comparison with previously reported data with a Q‐switched laser shows that the field strength required for intrinsic optical damage increases by almost one order of magnitude from 106 V/cm at 10−8 sec to over 107 V/cm at 1.5 × 10−11 sec. This is in qualitative agreement with published estimates based on the electron avalanche breakdown mechanism.

Method and apparatus for selective burnout trimming of integrated circuit units

Abstract: Supplementary metallized connection parts short-circuiting or connecting incremental sub-components of one or more circuit elements of an integrated circuit are laid down on the semiconductor slice at the same time as the usual metallized connection pattern is made. The components associated with the incremental sub-components are measured to determine the program of adjustment and selective burnout of the supplementary connections. The selective burnout is carried out by applying a sequence of pulses to the segments to be burned out under monitoring by a measuring circuit, which blocks the delivery of further pulses, either immediately or after one or a few more pulses, when the measuring circuit detects the opening of the connection. The process is preferably carried out on integrated circuits before the semiconductor slice on which they are made is separated into individual circuit units. The pulses are applied in sequences in which individual pulses or series of pulses have increasing amplitude and/or pulse duration and/or pulse frequency.

Nanosecond surface discharge study by using Dust figure techniques

Abstract: The developing mechanisms of the positive and negative corona streamers on the insulation surface have been studied by using the Dust figure technique together with a line pulser. The present method has the advantage of measuring the velocity of corona discharge development and the discharge mechanism, because the distributions of the positive and negative charges in the discharge figure can be colorfully separated and recorded. By applying shorter time pulses from 10‐ to 920‐nsec duration to a needle point where a glass plate is sandwiched in between the needle and plate electrodes, the diameter of the recorded discharge and the charge quantities and their distributions against the pulse duration were obtained. The observed average velocities of the developing corona streamers at a voltage of 12.0 kV were 2.05×108 cm/sec in the positive and 0.63×108 cm/sec in the negative, respectively. Moreover, when the negative pulse voltage was applied to the needle point the formation time lag of the cathode fall was about 10 nsec and the resulting high densities of the positive and the negative charges induced a back discharge.

Autoacceleration of an intense relativistic electron beam

Abstract: A novel autoacceleration mechanism was used to double the particle electron kinetic energy at the expense of pulse duration. Acceleration is accomplished by passing the beam through a cavity structure inserted into a conventional drift tube. Experimental resulsa showed that the mean electron kinetic energy was incresed from about 0.5 to 1.0 MeV, while the beam duration decreased from about 50 to 25 nsec. The total energy efficiency of the prceess wag approximately 75%. (auth)

Dimming circuit with saturated semiconductor device

Abstract: A fluorescent lamp is operated by a-c pulses having a pulse length sufficiently short that the lamp acts like slightly positive impedances A pulse modulator which produces the pulses has a power transistor biased to saturation However, varying the base drive of the saturated transistor causes a generally linear change in tube current to permit tube dimming and control A servo circuit provides feedback control of the base drive to automatically compensate for variable effects to maintain constant tube lighting Tube dimming is obtained by adjusting the feedback circuits of the servo

Investigation of the characterstics of a mode-locked Nd:Glass laser with the aid of a picosecond streak camera

Abstract: An infrared-sensitive streak camera, capable of resolving optical pulses of durations of ∼3 ps, has been used to analyze the temporal development of the individual picosecond pulses in a mode-locked pulse train. A progressive increase in the duration of the individual pulses throughout the pulse train is observed, the rate of increase in the pulse duration being an approximate quadratic function of the optical field. In addition, temporal analysis of the laser output signal, dispersively delayed with the aid of a grating pair, confirms the existence of phase-modulation effects during the development of the mode-locked pulse train.

Study of Self-Focusing and Self-Phase-Modulation in the Picosecond-Time Regime

Abstract: Study of the propagation of a single picosecond pulse of a mode-locked Nd-glass laser in CS2 nitrobenzene and toluene by observations of the birefringence and spectral changes in self-focused laser light. Multiple second-harmonic probing beams are used for birefringence measurements in a single IR pulse in various portions of the active cell. The orientational Kerr effect is found to be the prime factor of induced birefringence in nitrobenzene and toluene. The results for CS2 are also consistent with this mechanism and show that the duration of an IR pulse in the focal volume is less than that of the incident pulse. The properties of beams which are focused within the cell by an external lens are also investigated.

Vacuum-uv radiation of laser-produced plasmas

Abstract: The continuum radiation of laser-produced plasmas, from high-Z-material solid targets, has been studied experimentally in the range of 1000 to 2000 A, with special attention to 1216 A. The energy radiated per pulse was found to grow almost linearly with target irradiance, but more slowly with laser pulse length and wavelength. An ambient pressure of 10−1 torr is enough to reduce it considerably but it is weakly sensitive to focusing, target material, and laser incidence and observation angles. The absolute value of the radiance was measured in a number of cases. The highest spectral radiance obtained was 3.5 × 1022 photons s−1 cm−2 sr−1 A−1 at 1200 A, with a total of 3 × 1013 photons sr−1 A−1 per pulse, for a laser energy of 10 J. Possible ways of improving this figure are discussed. A light-condensing system is described which increases the uv irradiance at the point of utilization and makes an operational and competitive source.

Control of brushless D-C motors

Abstract: To control the operation of brushless d-c motors, in which armature coils are pulse-energized, a signal representative of voltage induced in the armature coils is obtained, this signal is separated into its a-c and its d-c components and the a-c component is inverted to derive an inverted 180* out-of-phase signal. The timing of the energization of the motor windings is controlled, with respect to angular position of the rotor, by the inverted a-c signal component, and the extent, or pulse width, or pulse duration of the energization is controlled in dependence on the d-c component.

Time resolution and characteristics of a broadband picosecond continuum and light gate

Abstract: A broadband continuum which last a few picoseconds can be generated in isotropic materials such as liquid H2O or D2O by single picosecond pulse excitation. It is demonstrated that the blue part of the spectrum is delayed relative to the red portion. A spectral analysis reveals a stimulated inverse Raman band around 260 cm−1 to the blue of the first anti‐stokes emission. We offer two alternative explanations for this observation. The open time of the light gate is shown to depend on various parameters and in the case of a CS2 shutter, it may be extended over much longer time intervals than the pulse duration. At the same time we have observed depolarization and isotropic scattering of the interrogating light.

Pulsed high-energy gamma rays from the Crab nebula.

Abstract: Review of recorded data on the pulsed radiation detected by the Cornell 100-inch gas-Cerenkov gamma-ray telescope within 1 degree of the Crab Nebula in direction, at hundreds of MeV up to more than 1 GeV, coincident in time with optical pulses from NP 0532. A main pulse and a secondary pulse are shown to contain about an equal number of events and display evidence of being narrower than at lower energies. There is weak evidence for further pulse structure in the interval between these two peaks, and also for an unmodulated gamma-ray component about equal to the time-averaged pulsed flux.

Pulse reflection type ultrasonic thickness meter

Abstract: A pulse reflection type ultrasonic thickness meter having an ultrasonic transducer which produces an ultrasonic pulse wave and transmits it to an object to be measured and receives an echo pulse from the object and includes an automatic gain control circuit to control the height of the echo pulse. A circuit is provided which controls the automatic gain control circuit when the echo pulse is smaller than a predetermined value, so that the echo pulse can be maintained substantially constant over a necessary range.

WC8 - Parametric studies of pulsed HF lasers using transverse excitation

Abstract: A detailed comparison of four types of electrode structures for HF laser action was made. The HF was produced by transverse discharges through SF 6 /RH mixtures. The pulse energy, pulse duration, and spectroscopic output were measured as a function of the type of hydrogen donor, its partial pressure as well as the total pressure when He was added. The hydrogen donors used were H 2 , CH 4 , C 2 H 6 , C 3 H 8 , and commercial gasoline.

Signal recognition circuitry

Abstract: Signal recognition circuitry provides a control signal which is initiated following the receipt of successive input signals provided they are spaced less than a first duration apart and have been received for at least a second duration with such control signal continuing for at least a third duration. A first pulse generator is controlled by the input signals and is used to assure that the spacing between pulses is proper by producing a pulse if the spacing is improper with such pulse being used to inhibit operation of a second pulse generator used to measure the second duration. The second pulse generator controls operation of a switching circuit and operation of a third pulse generator. If the second duration is satisfied, a pulse is provided by the second pulse generator causing the switching circuit to provide the control signal. The third pulse generator begins operation after the pulse has been provided by the second pulse generator and connects with the switching circuit to terminate the control signal in response to a pulse produced by the third pulse generator when it has been operating for said third duration.

Radio-frequency pulse generation system and method

Abstract: This disclosure is concerned with radio-frequency pulse generation, as for Loran type navigation transmissions and the like, wherein the transmitted pulse is generated by causing a pair of opposite poled half-cycle pulse generators to impulseexcite a tuned coupling network and antenna (or other load), the transfer function characteristics of which are adjusted to yield the desired pulse shape, with the complete cycle resulting from the pair of pulse generator half-cycles controlling, for example, the first two half cycles of the leading edge of the antenna pulse current, and the network and antenna characteristics controlling the remaining half cycles.

Digital pulse rate ramping circuits

Abstract: A circuit for digitally ramping the pulse repetition rate of a train of pulses is particularly useful for accelerating a stepping motor to or from its operating feed. In one mode of operation, the pulse ramp is linearly proportional to the difference between the instantaneous and desired pulse rates. In another mode of operation, a minimum pulse rate is impressed on the output pulse train. Means responsive to excessive, high rate input pulses bypass a portion of the circuit for preventing circuit overload.

Thermal blooming of pulsed laser radiation

Abstract: We have observed thermal blooming of focused 1.06‐μ pulsed laser radiation propagating in a weakly absorbing medium. Laser pulse lengths of 3–100 μsec were used to span the hydrodynamic time, which is defined as the pressure disturbance transit time across the laser beam. One‐dimensional eikonal models of laser propagation in the limits of pulse duration less than the hydrodynamic time and pulse duration greater than the hydrodynamic time agree well with the experimental results.

The Gamble I Pulsed Electron Beam Generator

Abstract: The Gamble I pulsed electron beam generator at NRL recently has undergone several major modifications. The modified generator has a nominal output into a matched 1.5-Ω load of 500 kA at 750 keV, with an 70-nsec (FWHM) pulse length and a 20-nsec (10%–90%) voltage risetime. The distinguishing characteristics of low prepulse (< 1%) and high reproducibility in output voltage and current (± 3%) result primarily from conversion from operation with self-breakdown water switches to operation with triggered high-pressure gas switches. Fast pulse risetime was maintained by using a low-inductance multichannel triggered output switch in conjunction with a new low-inductance vacuum diode with a radial insulator.

Apparatus for lengthening laser output pulse duration

Abstract: Apparatus for use with a laser oscillator having a short duration pulse output with high spectral purity for amplifying and lengthening the pulse output without loss of spectral purity. The apparatus typically includes a laser amplifier and means for applying radiation from the laser oscillator to the amplifier and for reapplying a predetermined portion of the amplifier output regeneratively to the amplifier to maintain it in an amplifying condition for a period several times longer than the duration of the original radiation pulse from the laser oscillator. A timing system is provided for synchronizing the application of laser oscillator radiation to the amplifier coincident with excitation of the amplifier to a lasing condition.

An Optimally Energized Cardiac Pacemaker

Abstract: Batteries that power implanted cardiac pacemakers deteriorate because of energy drain and permeation of body fluids. They must, therefore, be replaced periodically, most often by means of an operation. In this paper, the stimulating waveform that draws the least amount of energy from the battery and also delivers the minimum energy to a heart cell is derived. It is shown that a 31-percent reduction in energy (with respect to that required by the standard rectangular pulse) can be achieved if the pulse duration is about twice the cell time constant. Moreover, it is demonstrated that the required energy is insensitive to pulse-duration variations (due to component changes). An easily synthesized suboptimal approximation is developed and requires only slightly more energy than the optimal pulse.

System for the controlling of an apparatus for the electric discharge machining etc.

Abstract: Discrete electric-discharge pulses are applied across a dielectric-swept gap between an electrode and a workpiece by triggering an ON-OFF switch between its conductive and nonconductive states in accordance with parameters of the gap so that per pulse adaptive control of the individual machining discharges is effected. An integrator responsive to the gap current, may be used to operate the switch means which may be turned on upon the detection of a pilot discharge. The number of unsatisfactory discharges is detected and, if this number exceeds a predetermined level, is used to control a gap parameter. The integrator signal may be digitalized for accumulation in a counter controlling pulse duration and other parameters.

A Four‐Pulse NMR Experiment Using Maximum Pulse Width

Abstract: The classical four‐pulse experiment of Waugh, Huber, and Haberlen (WAHUHA) is extended to the upper limit in pulse width which is possible in the four‐pulse timing, i.e., the pulse width equals 1/6 of the cycle time. It is shown that coherent averaging is still in effect and high resolution in solids can be achieved to the same extent as in the δ pulse limit.

Superfluorescence in N2 and H2 electron‐beam‐stabilized discharges

Abstract: Previous N2 and H2 electronic transition lasers have been limited to short pulse durations (10−9–10−7 sec). Using an electron‐beam‐stabilized discharge in argon, nitrogen (or hydrogen), and hydrogen fluoride mixtures, we have observed repetitive superfluorescent pulses lasting 5–20 μsec. Optical‐cavity measurements verify that optical gain is present throughout the pulse duration at wavelengths in the nitrogen first‐ and second‐positive band systems and in a hydrogen near‐infrared band system. It is believed that HF serves to maintain a population inversion for a longer period of time by providing preferential collisional deactivation of the lower laser levels.

Pulse width selector

Abstract: An apparatus for accepting or rejecting pulses on the basis of pulse duration. Each pulse in an incoming pulse train is clocked into a first shift register, while a counter records the duration of the pulse. When the end of the pulse is recognized, the counter is checked to establish whether the pulse duration is within the predefined limits which have been established by the operator and set into the counting circuitry. If the pulse duration (width) is within the established limits, the pulse is shifted in parallel, out of the first shift register to a second shift register. If the pulse duration is outside the established limit, it is eliminated entirely (depending on the mode of operation). The first shift register is reset and is ready to receive the next pulse in the pulse train. The pulses in the second shift register are then shifted to an output line completing the selection process.

Electrical discharge machining process employing brass electrode, silicone oil dielectric, and controlled voltage pulses

Abstract: Electrical discharge machining process in which the parameters are controlled to provide higher metal removal rates than heretofore considered possible, together with maintenance of good surface integrity. Specifically, the new process makes use of a brass electrode, a silicone oil dielectric, and a pulsating voltage between the electrode and the workpiece, the pulses of the voltage having a pulse duration ranging from 4 to 200 microseconds and an on time of from 20 to 80 percent of the period of such pulses.

Filamentation in silicon‐on‐sapphire homogeneous thin films

Abstract: Dynamic temperature configuration and current filamentation in single‐crystal silicon films on sapphire substrates were studied with high‐amplitude constant‐current pulse excitation using Sunshine's stroboscopic technique. Temperature configurations vary greatly depending upon the pulse duration and amplitude, electrode geometry magnitude of heat flow into the substrate, and magnitude of transverse heat flow. Filamentation occurs in two steps, each accompanied by a voltage drop. An initial broad filament forms as local regions rise in temperature beyond the peak of the resistivity‐temperature curve of the silicon. The second filamentation is a narrow melt channel that forms interior to the initial filament. A time‐dependent computer simulation is presented that includes both the heat flow into the substrate and transverse heat conduction. The model shows that a stable‐current filament can exist without a melt transition, but only for a very restricted range of current levels.

MD2 - A high-pressure pulsed CO 2 chemical transfer laser

Abstract: The exothermic chain reactions between deuterium and fluorine were used to produce strong laser emission from carbon dioxide in a high-pressure pulsed transfer laser. The chemical chain reaction was initiated by flash photolysis of the reactive components. The active constituents were diluted in helium and premixed at temperatures of approximately -65°C to improve stability of the mixture. Peak-power outputs of 200 kW in pulses having duration of 30 μs have been observed in dilute mixtures at total pressures of one atmosphere. Energy outputs of up to 5 J, small signal-gain coefficients of 3 m-1and a chemical efficiency of 3 percent based on total gas volume have been obtained in this system. The output power, laser pulse duration, and delay are strongly dependent on partial pressures of the diluents and degree of refrigeration of the mixture. A kinetic model of the system has provided values for the gain coefficient, pulse duration, time of maximum gain, and power output in good agreement with the experiment.

Pulse width sensing circuit

Abstract: A circuit for producing an output signal indicative of the presence of an input signal of duration greater than a given duration, T. The circuit includes a first stage which in response to a sampling pulse and the presence of an input signal of first value, stores a signal of first binary significance. The circuit also includes a second stage which in response to a shift pulse occurring a time T after the sampling pulse produces at its output, which is the circuit output, a signal corresponding to the one stored in said first stage. Each stage includes means responsive to the input signal for resetting the output of each stage to a level of second binary significance when the input signal has a second value. A signal of first value must, therefore, be present for a duration greater than T to produce an output of first binary significance, where the duration must also include a sampling pulse followed by a shift pulse. The circuit also includes means for, selectively, directly passing the input signals from the input to the output of the circuit.